1. Field of the Invention
The invention relates to a machine tool, in particular a wood-working machine, with a tool for chip removal rotating in direction of rotation D and a suction hood covering the tool with a partially opened circumferential wall that has a radial spacing A from the tool and a suction nozzle for suctioning off chips.
2. Discussion of Background Information
In known embodiments of suction hoods, the flow conditions in the hood vary substantially between the idling and processing conditions. During processing, the hood opening through which the tool interacts with the workpiece is largely closed by the workpiece. As a result, insufficient air flows into the hood, and the flow in the hood breaks down. Uncontrolled turbulences develop.
Suction hoods of this type generally have a straight hood wall running tangentially to the tool circumference in the chip intake area, so that the spacing from the tool in the direction of rotation first decreases and then increases again. A back pressure thus forms before the narrowest cross section, against which back pressure the chips have to be transported.
In particular low-mass chips and particulates that have only a low kinetic energy and therefore have to be guided and transported with the air flow inside the hood, are not adequately captured. On the one hand, they do not arrive in the hood at all or they rotate with the tool in the hood and then escape again. Undefined flow conditions prevail in the area behind the outlet opening for the chips, since here the flow of suction air and the tool's own ventilation more or less cancel one another out. These problems occur particularly in the processing of MDF, rigid foam and gypsum-bound or cement-bound materials when the powdered portion of the chips predominates or the chips have a low mass.
A machine tool, in particular a wood-working machine, is known from DE 100 49 500 A1, with a tool for chip removal having at least one cutting edge and a suction hood covering the tool with a partially opened circumferential wall and a suction connection for suctioning chips. The circumferential wall of the suction hood is embodied in a conically or spherically curved form in the area of the rotational plane of the at least one cutting edge of the tool and the suction connection is arranged in the area of the largest diameter.
In the case of low-mass chips and particulates that have only a low kinetic energy, there is a danger that they will be captured only inadequately and will not arrive in the hood or will leave the hood again after the revolution of the tool. The area located behind the outlet opening for the chips in the direction of rotation is problematic, since here the direction of movement of the tool cutting edges runs counter to the suction direction and the two flows cancel one another out to a certain extent. Particles that have flown past the outlet opening can no longer be suctioned and leave the hood again through the processing opening. In the case of low-mass chips and particulates it does not help either to provide the conical shape of the interior wall for a second, axially displaced chip circulation, since a certain kinetic energy of the particles is necessary for this chip circulation.